Dolores River Desert Bighorn Sheep Herd (DBS-61)

Executive Summary GMUs: S-63 (Middle Dolores River) and S-64 (Upper Dolores River) Tier Status: Tier 1 Land Ownership: BLM 45%, Private 29%, USFS 24%, State 2%, 2018 Posthunt Population Estimate: 175 Average Length of Longest Horn (harvested rams): 31 “

Posthunt Population Estimate

300 Dolores River Herd

250

200

150

100

50

0

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Proposed Objective S63 S64 Dolores Herd

Figure 1. DBS-61 posthunt population estimate 1987-2019.

Background and Issue Summary: The Dolores River Desert Bighorn sheep herd (DBS-61) is located in southwest Colorado and occupies the canyon country of the Dolores River, and its tributaries, downstream of McPhee Reservoir. It consists of Game Management Units (GMUs) S-63 (Middle Dolores River) and S-64 (Upper Dolores River). The majority of the occupied bighorn habitat occurs on lands managed by the Bureau of Land Management (BLM). DBS-61 is a Tier 1 bighorn population and should be given the highest priority for inventory, habitat protection and improvement, disease prevention and research.

Although bighorn sheep were likely indigenous, none were present in the past century. The current population was established beginning in 1986 with the release of 25 bighorn from Arizona. There have been a total of four transplants of desert bighorn into the Dolores Canyon. Population sources have been from Arizona (source for two transplants), Nevada, and Utah. Since the initial transplant, the population of bighorn in the Dolores Canyon has grown and peaked at an estimated 235 animals in 2001. At that time, there was a sharp decline in the population and the cause was never determined. The population has since gradually increased and is now estimated at 175.

Inventory of the population is done by coordinated ground surveys and helicopter surveys. The coordinated ground surveys are done annually in late spring. Helicopter surveys are done every three to five years. Timing of aerial surveys vary throughout the year. Data provides some indication of herd performance and distribution. Because of the low density of bighorn and vast amount of country, minimal numbers of bighorn are located and classified, providing inconsistent data between survey efforts.

The Dolores River Bighorn herd offers limited ram hunting. The first licenses (two) were in 1993 and were valid only in S-64. Ram hunting in S-64 has been continuous since then and began in S-63 in 2010 when licenses were valid for both units. There are currently (2019) five ram licenses available, two in S-63 and three in S-64. Success rates generally run 100% annually. Ewes have not been hunted, but with an increasing population, the opportunity exists to introduce ewe licenses in the DAU.

Management Objectives Public Involvement: A public survey was used to guide recommendations presented in this HMP. Over 130 individuals participated in the survey either on the internet or by paper copies. The majority of respondents wanted to see an increase in the population size and were happy with the current management of ram hunting opportunity.

Population Size: The current population estimate for DBS-61 is 175 bighorn and increasing. Factors adversely affecting the population include habitat quality, predation, and recreation disturbance. The population is still short of highest recorded size of 235. Based on available habitat and the current health of the population, the population has the potential to increase. Three population objective alternatives are proposed, with alternative 2 being the staff recommendation:

1) Alternative 1- 150-250, stable population objective with current population in the middle of the range 2) Alternative 2- 175-275, stable to increasing objective with current population at bottom of objective range 3) Alternative 3- 200-300, increasing objective with current population below objective range

Harvest Objective: Ram Harvest: The length measurement of horns on harvested rams provide an index to the age and trophy quality of harvested rams. The greater the average horn length, the higher the trophy quality. This comes at the cost of restricting hunter numbers to produce more and bigger rams. A smaller average horn length allows more hunter opportunity at the cost of decreasing the number of rams in the population and subsequently the potential trophy quality. The current average length of the longest horn on harvested rams is 31”. Three alternatives for the length of the longest horn on harvested rams are proposed, with staff recommending alternative 2 which is similar to current management:

1) Maintain a running average horn length under 31 ½” of harvested rams over a three year period (stable to increasing hunting opportunity), 2) Maintain a running average horn length between 28” to 33” of harvested rams over a three year period (stable hunting opportunity), or 3) Maintain a running average horn length over 30” of harvested rams over a three year period (stable to decreasing hunting opportunity)

Ewe Harvest: Ewe removal from the population via translocation or hunter harvest will be considered when the population meets the criteria set forth in Colorado’s Bighorn Sheep Management Plan (George et al 2009). Ewe harvest is a population management tool to maintain healthy populations of bighorn sheep and for hunter opportunity. It also assists biologists in gaining more observational data from ewe hunters regarding herd composition and distribution.